1. Field of the Invention
This invention relates to a method and an apparatus for forming letter sheets.
2. Description of the Related Art
Mass mailings generally rely upon apparatus to feed, cut and fold a continuous form into folded letter sheets for stuffing in an envelope. The continuous form is typically provided in a paper web having pin hole edges for tractor feeding of the web. Furthermore, the web may be perforated across its width at uniform intervals; in such case, the paper web is often referred to as "computer paper". One method of handling a paper web (with or without the noted transverse perforations) is as follows. The paper web is tractor fed to a separating station (if the web is transversely perforated) or a cutting station (if the web is not transversely perforated) and the separate sheets are then conveyed to a folding station whereat automatic arms first fold one marginal portion of the sheet over a medial portion of the sheet and then fold the remaining marginal portion of the sheet over the first mentioned marginal portion and the medial portion of the sheet. This results in a folded letter which has a standard letter fold. One drawback with this method is that once the individual sheets have been cut or separated from the continuous form it is difficult to keep them in registration in order to make the letter folds properly. Furthermore, once cut or separated, the sheets are generally supported underneath which makes a Z-fold for the sheets problematic. By way of explanation, a Z-fold results when one marginal portion of the sheet is folded over the medial portion of the sheet and the other marginal portion of the sheet is folded under the medial portion of the sheet. A Z-fold has an advantage in mass produced letters in that the address at the head of the letter may be on the outside of the letter so that it may appear under a window in an envelope into which the letter is stuffed.
A second method of forming folded letters from the aforenoted paper web involves tractor feeding the web and then buckle folding the leading portion of the web subsequent to which the leading portion is severed from the web resulting in a folded letter sheet. One drawback with this approach is that it cannot be used where inserts have been adhered to the web ahead of the buckle folding station if such inserts are of significant thickness. Thus, for example, this method cannot be used where standard thickness credit cards (which are about 30 thousandth's of an inch in thickness) are attached to each sheet in the continuous form since the continuous form will then jam in the buckle folding rollers.
While not known to be used in the mass production of letter sheets, it is known to progressively fold webs along their length with edge guides which progressively urge a marginal portion of the web towards the center of the web. If this method were employed in the folding of the aforenoted paper web of computer paper (which typically has a width of about 91/2 inches), it would require about an eight-foot run to complete a fold of a marginal portion of the web over the medial portion of the web without ripping the paper or causing it to separate at any transverse perforations. Space is generally extremely limited in mail rooms. This method would, therefore, be unsuitable in many mass mailing applications due to the large area that would be taken up by such machinery.
Accordingly, there remains a need for a method and apparatus for forming letter sheets more suitable for use in the mass production of letters.